In order to adapt to the increasing data transmission demands and relieve the load of a wireless network, an existing upgrading technology is to increase spectrum resources, so as to transmit more information. For a spectrum that is strictly controlled by a spectrum management organization, spectrums that are obtained by purchasing a license are difficult to be continuously distributed, and a data transmission peak rate needs to be improved by using a spectrum resource fragment technology. A wireless device can use a free spectrum as long as the wireless device meets a power limit. Generally, a particular signal to noise ratio is required in data transmission in wireless communications, and the free spectrum may be used by some devices at any time. Therefore, when the free spectrum is used for communication, a data transmission peak rate also needs to be improved by using the spectrum resource fragment technology.
As data communications rapidly develops, the 802.11 standard is applied to more scenarios and has a broader market. Because network resources used for data transmission are limited, and the 802.11 standard is based on a carrier sense multiple access/collision detect (CSMA/CA for short) mechanism, a quality of service (QoS for short) problem occurs as long as network resource contention exists. First, because of an increase of a data transmission amount and detailed data service classification, higher requirements are put forward on transmission resource allocation, a transmission delay, a data packet loss rate, and a delay variation. Second, because total transmission resources are limited, if a type of service occupies more transmission resources to transmit data, fewer transmission resources can be used by another service to transmit data. Therefore, higher requirements are also put forward on planning and allocation of transmission resources of various services in an 802.11 network. A scheduling transmission manner can exactly well resolve the QoS problem, and needs to be compatible with a legacy wireless local area network system. Therefore, a scheduling transmission solution needs to be provided in a contention transmission system.
In an 802.11 system, the following hidden node problem and exposed node problem exist. The hidden node problem refers to that when a first access point (AP for short) 1 transmits data to station (STA for short), an AP2 does not know about this and also starts to transmit data to the STA. As a result, the STA cannot receive the data of the AP1 correctly. The exposed node problem refers to that when a STA1 transmits data to an AP1, a STA2 senses a network allocation vector (NAV for short) that is set when the STA1 sends the data, so the STA2 cannot transmit data to an AP2; however, data sending by the STA2 does not affect receiving by the AP1 in this case, and consequently, system resource usage is reduced. These problems all lead to that contention transmission cannot be normally performed.